The family of slain publisher Shahzahan Bachchu have started a case naming four unidentified people as suspects over the murder of the free-thinking writer in Munshiganj.Bishakha Prokashoni owner Bachchu's second wife 'Afsana' initiated the charges at Sirajdikhan Police Station on Tuesday, OC Md Abul Kalam said.Quoting witnesses, police said four assailants on two motorbikes shot Bachchu dead at Kakaldi, his ancestral village, on Monday afternoon.The 65-year-old former president of Munshiganj unit of the Communist Party of Bangladesh received threats from religious extremists for his writings on the social media, people close to Bachchu said.He was also the acting editor of locally published weekly Amader Bikrampur. A team of Counterterrorism Unit of Police from Dhaka visited the scene along with other top police officials of Munshiganj on Monday night.Police are yet to name any suspect.